Professional Pilot, May 2018

Arterial oxygen saturation levels hypoxia symptoms vs altitude Circulatory central nervous system failure Convulsions Cardiovascular collapse 90 80 80 70 70 60 Previously unrecognized cardiovascular diseases may be unmasked by lack of blood oxygen a problem for both crew and passengers Watch for symptoms of developing hypoxia such as breathlessness excessive yawning fatigue but also euphoria and the inability to perform well trained tasks and finally unconsciousness Fatal cases of decompression There are 2 well documented cases where a slow decompression resulted in the loss of all occupants In the summer of 2005 a Boeing 737 300 operated by Helios Airways slowly lost cabin pressure while climbing enroute from LCA Larnaca Cyprus to PRG Prague Czech Republic While the crew was incapacitated the aircraft flew initially as programmed on autopilot and then crashed close to Marathon Greece All 121 persons aboard perished That morning the pressurization system was set to manual on the overhead panel after maintenance activity Several checks by the flightcrew didnt discover and fix this error They were clearly not familiar enough with the aircraft and ignored or completely misunderstood several system warnings The passenger oxygen masks deployed automatically at a cabin altitude of 18000ft The captain was trying to communicate with ground engineers but he was clearly 66 PROFESSIONAL PILOT May 2018 showing signs of hypoxia already and was unable to think or speak clearly After both pilots passed out Greek F 16s observed a flight attendant with a CPL license entering the cockpit with a portable oxygen mask However his skills were not sufficient in this situation and his heroic effort failed in catastrophe Early recognition of hypoxia could have avoided those deaths In the US the 1999 crash of a Learjet 35 N47BA in South Dakota is a prime example of slow and unnoticed hypoxia onset Enroute from Orlando to Dallas the aircraft lost cabin pressure and all aboard fell unconscious The aircraft flew for almost 4 hours and finally crashed in South Dakota near Aberdeen PGA Golfer Payne Stewart and his team were on board 4 passengers and 2 crew perished The failure of both pilots to quick don their oxygen masks and breath emergency crew oxygen may only be explained by a slow and unnoticed onset of hypoxia causing their inability to think and act Simulator training lacks diversity In sim training we almost always deal with rapid explosive decompression A nice bang is heard in the simulator and the procedure is performed without too much thinking oxygen masks on passenger oxygen on emergency descent mayday call and alert surrounding aircraft At or below 10000 ft masks are taken off all is reset to normal and then on to the next simulator scenario However training for the Tibetan Plateau is different The briefing is extensive and includes a discussion of turn radius and escape routes Turn radii at jet speeds and high altitudes are so wide that they may exceed airway and thus Minimum Enroute Altitude MEA width At any point during the 500 nm transit over the Tibetan Plateau pilots have to know their plan of action Escape routes are charted on the map and lead through the least high terrain valleys to the north and usually end in a diversion to URC Ürümqi China after up to 2 hours of diversion time A diversion to the south is impossible as the main Himalayan range means even higher terrain Emergency descent may only be conducted to the MEA of the escape route which means usually around 20000 ft Passengers may need to breath supplemental oxygen for periods exceeding 15 minutes which requires the installation of extra oxygen bottles on aircraft used for these routes Some escape routes even require a climb later on meaning that while passenger oxygen may be shut off after 20 minutes when altitude is sufficient in order to conserve supplies itll have to be turned on again later as MEAs rise again as we continue to Ürümqi This morning all went well A beautiful sunrise over the peaks of Gongga Shan mountain at almost 25000 ft a significant and welcome marker signaled the eastern rim of the Himalaya and the much lower lands of Szechuan While our transit of Tibet was uneventful we were well prepared for emergencies at all times It should be remembered that on other routes such as over Greenland or parts of South America aircraft also fly over high terrain that wont allow a quick descent to breathable altitudes Be prepared The effects of altitude on the body dont change in a linear fashion but increase exponentially While TUC at 20000 ft may be 20 minutes its only 3 min at 30000 ft and seconds at 40000 ft Peter Berendsen flies a Boeing 747 as a captain for Lufthansa Airlines He writes regularly for Pro Pilot on aviation related subjects 25000 ft 98 90 02 Saturation Stage Indifferent Compensatory Disturbance Critical 20000 ft 15000 ft 10000 ft 5000 ft Decrease in night vision Impaired judgement coordination efficiency Impaired flight control Impaired handwriting speech Decreased coordination Death Drowsiness

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